2 Answers
2

when the mouse is on, either it just stays still or not, or you click it or not, it conserves around ~1mA (average of active and idle modes);

when you move the mouse, if the mouse is optical, the led at the bottom side of the mouse is lit, and it conserves additional ~10mA for low-power leds and ~20mA for typical ones (let's take average 15mA);

when you don't use the mouse at all, it's tiny microcontroller will sleep and wait for interrupts (buttons / optical sensor), which basically will also will drain battery, but very minimal (like ~0.07mA - tinyAVR sleep power);

and sure, if you push the off button on the bottom side of the mouse, it will be completely turned off (you will need to press the same button again to make it work - my wireless logitech mouse has this button, others may not)

Some math:

Considering you're working with that mouse 10 hours a day, and you move it half of that time, and your mouse is sleeping for rest 14 hours of day, you get: